Teens are notorious for wanting to stay up late and for not wanting to get up early. If your teen is no exception, find out what's behind this behavior and how you can help him or her get better sleep — starting tonight.

Everyone has an internal clock that influences body temperature, sleep cycles, appetite and hormonal changes. The biological and psychological processes that follow the cycle of this 24-hour internal clock are called circadian rhythms. Puberty changes a teen's internal clock, delaying the time he or she starts feeling sleepy and awakens.

Most teens need about nine hours of sleep a night — and sometimes more — to maintain optimal daytime alertness. But few teens actually get that much sleep regularly, thanks to factors such as part-time jobs, early-morning classes, homework, extracurricular activities, social demands, and use of computers and other electronic gadgets.

Sleep deprivation might not seem like a big deal, but it can have serious consequences. Tired teens can find it difficult to concentrate and learn, or even stay awake in class. Too little sleep also might contribute to mood swings and behavioral problems. Drowsy driving can lead to serious — even deadly — accidents.

If your teen isn't getting enough sleep, there are a few things that you can try to help. For example:

Stick to a schedule. Tough as it might be, encourage your teen to keep weekday and weekend bedtimes and wake times within two hours of each other. Prioritize extracurricular activities and curb late-night social time as needed. If your teen has a job, limit working hours to no more than 16 to 20 hours a week.

Nix long naps. If your teen is drowsy during the day, a 30-minute nap after school might be refreshing. Be cautious, though. Too much daytime shut-eye might only make it harder to fall asleep at night.

Curb the caffeine. A jolt of caffeine might help your teen stay awake during class, but the effects are fleeting — and too much caffeine can interfere with a good night's sleep.

Keep it calm. Encourage your teen to wind down at night with a warm shower, a book or other relaxing activities.

Know when to unplug. Take the TV out of your teen's room. Minimize use of electronics in the hour before bedtime.

Adjust the lighting. If your teen does use a phone or tablet near bedtime, tell him or her to turn down the brightness and hold the device at least 14 inches (36 centimeters) away to reduce the risk of sleep disruption. In the morning, expose your teen to bright light. These simple cues can help signal when it's time to sleep and when it's time to wake up.

In some cases, excessive daytime sleepiness can be a sign of a problem, including:

Medication side effects. Many medications — including over-the-counter cold and allergy medications and prescription medications to treat depression and attention-deficit/hyperactivity disorder — can disrupt sleep.

Insomnia or biological clock disturbance. If your teen has trouble falling asleep or staying asleep, he or she is likely to struggle with daytime sleepiness.

Depression. Sleeping too much or too little is a common sign of depression.

Obstructive sleep apnea. When throat muscles fall slack during sleep, they stop air from moving freely through the nose and windpipe. This can interfere with breathing and disrupt sleep. You might notice loud snoring or intermittent pauses in breathing, often followed by snorting and more snoring.

Restless legs syndrome. This condition causes a "creepy" sensation in the legs and an irresistible urge to move the legs, usually shortly after going to bed. The discomfort and movement can interrupt sleep.

Narcolepsy. Sudden daytime sleep, usually for only short periods of time, can be a sign of narcolepsy. Narcoleptic episodes can occur at any time — even in the middle of a conversation. Sudden attacks of muscle weakness in response to emotions such as laughter, anger or surprise are possible, too.

If you're concerned about your teen's daytime sleepiness or sleep habits, contact his or her doctor. If your teen is depressed or has a sleep disorder, proper treatment can be the key to a good night's sleep.

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